The present invention relates to a plasma processing method and apparatus for use in dry etching, sputtering, plasma CVD, and the like and, more particularly, to a plasma processing method and apparatus of a high frequency induction system.
In recent years, to effect processing or the like on a semiconductor element at a high aspect ratio by a dry etching technique or effect burying or the like at a high aspect ratio by a plasma CVD technique, coping with developing dimensional fineness of semiconductor elements, it has been required to effect plasma processing in higher vacuum.
For instance, in the case of dry etching, when a high density plasma is generated in high vacuum, there is a reduced possibility of collision between ions and neutral radical particles in an ion sheath formed on a substrate surface, and therefore directions of the ions are aligned toward the substrate surface. Furthermore, because of a high degree of electrolytic dissociation, there results a high incident particle flux ratio of ions to neutral radicals arriving at the substrate. For the above-mentioned reasons, etching anisotropy is improved by generating high density plasma in high vacuum, thereby allowing processing to be achieved at a high aspect ratio.
Furthermore, in the case of plasma CVD, when a high density plasma is generated in high vacuum, an effect of burying and flattening a fine pattern can be obtained by the sputtering effect with ions, thereby allowing burying to be achieved at a high aspect ratio.
As one such plasma processing apparatus capable of generating a high density plasma under high vacuum there has been known a plasma processing apparatus of a high frequency induction system such that plasma is generated within a vacuum vessel by applying a high frequency voltage to a planar spiral discharge coil. A plasma processing apparatus of this system causes a high frequency magnetic field to be generated within the vacuum vessel so that an induction electric field is generated through the high frequency magnetic field within the vacuum vessel to accelerate electrons for plasma generation. As such, by increasing the intensity of the current flowing across the coil it is possible to generate high density plasma under high vacuum, thus obtaining sufficient processing rate.
A plasma processing apparatus of the high frequency induction system is shown by way of example in FIG. 8. In FIG. 8, evacuation is effected while a suitable gas is being introduced into a vacuum vessel 1, and a high frequency voltage is applied by a high frequency power source 2 for discharge coil to a planar spiral discharge coil 4 disposed on a dielectric plate 3 while the interior of the vacuum vessel 1 is kept under adequate pressure, whereupon plasma is generated within the vacuum vessel 1, it being thus possible to carry out plasma processing in connection with such operations as etching, deposition, and surface modification with respect to a substrate 6 placed on an electrode 5. In this case, a high frequency voltage is applied to the electrode 5 by a high frequency power source 7 for electrode, as shown in FIG. 8, whereby ion energies reaching the substrate 6 can be controlled.
However, with the conventional system shown in FIG. 8, one issue is that a large quantity of a reaction product deposits on the dielectric plate, which gives rise to dust generation and maintenance cycle deterioration. Another issue is that the atmosphere within the vacuum vessel is not stabilized, with the result that the system can only exhibit poor reproducibility in plasma processing.
More specifically, in the case of plasma CVD, in the course of thin film deposition on the substrate, similar thin films deposit also on the dielectric plate. In the case of dry etching, substances produced through an etching reaction and/or a vapor phase reaction may become thin-filmed on the dielectric plate. In the course of processing cycles being repeated, such film deposits grow in thickness and, when the thickness of such film deposit exceeds a certain level, peeling may occur due to film stress, resulting in peeled films falling on the substrate in the form of dust. In the conventional system shown in FIG. 8, dust generation is likely to occur when only a small number of substrates is processed and this requires frequent cleaning (maintenance) of the dielectric plate with pure water or ethanol.
In the course of processing cycles being repeated, changes occur in the thickness of film deposition as already mentioned, and this results in changes in radical adsorption and in the atmosphere within the vacuum vessel, that is, partial pressures of reaction species, which adversely affect the reproducibility of plasma processing. An increase in the temperature of the dielectric plate due to heating by high energy ions impinging upon the dielectric plate is also a cause of a change in the rate of radical adsorption.
Moreover, with the conventional system shown in FIG. 18, another issue is that as cycles of processing are repeated in succession, the temperature of the dielectric plate 3 rises due to heating by high energy ions impinging upon the dielectric plate 3, with the result that the adhesion bond between the discharge coil 4 and the dielectric plate 3 is removed, which gives rise to deformation of the discharge coil 4. It has been found from experiments that if electric discharge is effected continuously for one hour by using Ar gas, the temperature of the dielectric plate 3 will rise up to 200.degree. C.
Then, it was conceived to bond the discharge coil 4 to a ceramic plate or glass plate 15 as shown in FIG. 19, then mounting the ceramic plate or glass plate 15 on the dielectric plate 3. However, there occurred an issue that the discharge coil 4 expanded due to temperature rise with the result that the ceramic plate or glass plate 15 became fractured.
If the discharge coil 4 is deformed, the distribution density of plasma within the vacuum vessel 1 will become changed and this will deteriorate in-plane uniformity of processing. Any breakage caused to the ceramic plate or glass plate 15 may not only result in the deformation of the discharge coil 4, but also may lead to abnormal electric discharge in the atmosphere.